Communication devices such as terminals are also known as e.g. User Equipments (UE), mobile terminals, wireless terminals and/or mobile stations. Terminals are enabled to communicate wirelessly in a cellular communications network or wireless communication system, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two terminals, between a terminal and a regular telephone and/or between a terminal and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the cellular communications network.
Terminals may further be referred to as mobile telephones, cellular telephones, laptops, or surf plates with wireless capability, just to mention some further examples. The terminals in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another terminal or a server.
The cellular communications network covers a geographical area which is divided into cell areas, wherein each cell area being served by an access node such as a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the terminals within range of the base stations. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the mobile station. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the mobile station to the base station.
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
3GPP LTE radio access standard has been written in order to support high bitrates and low latency both for uplink and downlink traffic. All data transmission is in LTE controlled by the radio base station.
3GPP/WLAN Interworking
Most current WLAN deployments are totally separate from cellular networks, and may be seen as non-integrated from a UE perspective. In this document, the terms “WLAN” and “Wi-Fi” will be used interchangeably. Most Operating Systems (OSs) for UEs, such as Android™ and ioS®, support a simple Wi-Fi offloading mechanism where a UE immediately switches all its IP traffic to a Wi-Fi network upon a detection of a suitable Wi-Fi network with a received signal strength above a certain level, e.g. above a certain threshold. Henceforth, the decision to offload to a Wi-Fi or not is referred to as access selection strategy and the term “Wi-Fi-if-coverage” is used to refer to the aforementioned strategy of selecting Wi-Fi whenever such a network is detected.
There are several drawbacks of the “Wi-Fi-if-coverage” strategy.
Though the user, such as a UE, may save previous pass codes for already accessed Wi-Fi Access Points (APs), hotspot login for previously non-accessed APs usually requires user intervention, either by entering the pass code in Wi-Fi Connection Manager (CM) or using a web interface. The connection manager is a piece of software on a UE that is in charge of managing network connections of the UE, taking into account user preferences, operator preferences, network conditions, etc.
A first drawback of the Wi-Fi-if-coverage strategy is that no consideration of expected user experience is made, except those considered in the UE implemented proprietary solution. This may lead to the UE being handed over from a high data rate cellular network connection to a low data rate Wi-Fi connection. Even though the UE's OS or some high level software is smart enough to make the offload decisions only when the signal level on the Wi-Fi is considerably better than the cellular network link, there may still be limitations on the backhaul of the Wi-Fi Access Point (AP) that may end up being the bottleneck.
A second drawback of the Wi-Fi-if-coverage strategy is that no consideration of the load conditions in the cellular network and the Wi-Fi network is made. As such, the UE may be offloaded to a Wi-Fi AP that is serving several UEs while the cellular network, e.g. LTE, to which the UE previously was connected to is rather unloaded.
A third drawback of the Wi-Fi-if-coverage strategy is that interruptions of on-going services may occur due to the change of IP address when the UE switches to the Wi-Fi network. For example, a user who started a Voice over IP (VoIP) call while connected to a cellular network is likely to experience a call drop when arriving home and the UE automatically switches to the Wi-Fi network. Though some applications, e.g. Spotify®, are smart enough to handle this and survive the IP address change, the majority of current applications do not. This places a lot of burden on application developers if they have to ensure service continuity.
A fourth drawback of the Wi-Fi-if-coverage strategy is that no consideration of the UE's mobility is made. Due to this, a fast moving UE may end up being offloaded to a Wi-Fi AP for a short duration, just to be handed over back to the cellular network. This is specially a problem in scenarios like cafes with open Wi-Fi, where a user walking by or even driving by the cafe might be affected by this. Such ping pong between the Wi-Fi network and the cellular network may cause service interruptions as well as generate considerable unnecessary signalling, e.g. towards authentication servers.
Recently, Wi-Fi networks have been subject to increased interest from cellular network operators, not only as an extension to fixed broadband access. The interest is mainly about using the Wi-Fi technology as an extension, or alternative to cellular radio access network technologies to handle the always increasing wireless bandwidth demands. Cellular operators that are currently serving mobile users with, e.g., any of the 3GPP technologies, LTE, UMTS/WCDMA, or GSM, see Wi-Fi as a wireless technology that may provide good support in their regular cellular networks. The term “operator-controlled Wi-Fi” points to a Wi-Fi deployment that on some level is integrated with a cellular network operators existing cellular network and where the 3GPP radio access networks and the Wi-Fi wireless access may even be connected to the same core network and provide the same services.
There is currently quite intense activity in the area of operator-controlled Wi-Fi in several standardization organizations. In 3GPP, activities to connect Wi-Fi access points to the 3GPP-specified core network is pursued, and in Wi-Fi alliance, WFA, activities related to certification of Wi-Fi products are undertaken, which to some extent also is driven from the need to make Wi-Fi a viable wireless technology for cellular operators to support high bandwidth offerings in their networks. The term Wi-Fi offload is commonly used and points towards that cellular network operators seek means to offload traffic from their cellular networks to Wi-Fi, e.g., in peak-traffic-hours and in situations when the cellular network for one reason or another needs to be off-loaded, e.g., to provide requested quality of service, maximize bandwidth or simply for coverage.
RAN Level Integration
3GPP is currently working on specifying a feature and a mechanism for WLAN/3GPP Radio interworking which improves operator control with regard to how a UE performs access selection and/or traffic steering between 3GPP and WLANs belonging to the operator or its partners. It may even be so that the mechanism may be used for other, non-operator, WLANs as well, even though this is not the main target.
It is discussed that for this mechanism the RAN provides assistance parameters that helps the UE in the access selection and/or traffic steering. The RAN assistance information is composed of three main components, namely threshold values, Offloading Preference Indicator (OPI) and WLAN identifiers. The UE also has rules and/or policies that make use of these assistance parameters.
The thresholds values may be for example for metrics such as 3GPP signal related metrics: Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ), Received Signal Code Power (RSCP), Energy per chip over the Noise (EcNo), and/or WLAN signal related metrics such as Received Channel Power Indicator (RCPI), Received Signal to Noise Indicator (RSNI), Received Signal Strength Indicator (RSSI), WLAN load/utilization, WLAN backhaul load/capacity, etc. One example of a RAN rule that uses the threshold value may be that the UE should connect to a WLAN if the RSRP is below the signalled RSRP threshold at the same time as the WLAN RCPI is above the signalled RCPI threshold. It is also discussed that the RAN should provide thresholds for when the UE should steer traffic back from WLAN to 3GPP. The RAN rules and/or policies are expected to be specified in a 3GPP specification such as TS 25.304 v12.1.0/TS 36.304 v12.0.0 and/or TS 25.331 v12.1.0/TS 36.331 v12.1.0.
With the above mechanism it is likely not wanted, or maybe not even feasible, that the UE considers any WLAN when deciding where to steer traffic. For example, it may not be feasible that the UE uses this mechanism to decide to steer traffic to a WLAN not belonging to the operator. Hence it has been proposed that the RAN should also indicate to the UE which WLANs the mechanism should be applied for by sending WLAN identifiers.
The RAN may also provide additional parameters which are used in Access Network Discovery and Selection Function (ANDSF) policies. ANDSF is an entity within an Evolved Packet Core (EPC) of a System Architecture Evolution (SAE) for 3GPP compliant mobile networks. The purpose of the ANDSF is to assist a UE to discover non-3GPP access networks, such as Wi-Fi or WIMAX, which may be used for data communications in addition to 3GPP access networks, such as High Speed Packet Access (HSPA) or LTE, and to provide the UE with rules policing the connection to these networks. One proposed parameter is Offloading Preference Indicator (OPI). One possibility for OPI is that it is compared to a threshold in the ANDSF policy to trigger different actions, another possibility is that OPI is used as a pointer to point, and select, different parts of the ANDSF policy which would then be used by the UE.
The RAN assistance parameters, i.e. thresholds, WLAN identifiers, OPI, provided by RAN may be provided with dedicated signalling and/or broadcast signalling. Dedicated parameters may only be sent to the UE when having a valid RRC connection to the 3GPP RAN. A UE which has received dedicated parameters applies dedicated parameters; otherwise the UE applies the broadcast parameters. If no RRC connection is established between the UE and the RAN, the UE may not receive dedicated parameters.
In 3GPP, it has been agreed that ANDSF should be enhanced for 3GPP Release-12 to use the thresholds and OPI parameters that are communicated to the RAN, and that if enhanced ANDSF policies are provided to the UE, the UE will use the ANDSF policies instead of the RAN rules and/or policies, i.e. the ANDSF has precedence.